Optical fibers with very low loss are used for medium and long haul transmission of optical signals. They typically transmit a single mode in a small core. To provide optimum light guiding properties for low loss the refractive index profile of the optical fibers is often complex, usually with an up-doped (with respect to pure silica) core, and multiple cladding layers. In contrast, many optical fibers for short haul applications, e.g., meters to tens of meters, are multimode fibers with simpler designs and attendant lower cost. These optical fibers typically have larger cores and carry higher optical power, but do not require optimum optical transmission efficiency. A main goal of these designs is ease of manufacture leading to lower unit cost.
One of these simple multimode designs has a step index with a pure silica core and a single down-doped cladding. This design contrasts with most single mode optical fiber designs that have a graded up-doped core and multiple layers of cladding. Thus this optical fiber is significantly less expensive to manufacture.
Although this step index multimode optical fiber is inherently simple and cost effective to manufacture, further cost reduction is a continual goal.